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Biomedical subjects

Theodore Eliades

Publications and source records attributed to Theodore Eliades.

33 records · Page 2Linked to original sources
PubMed2004

Materials-induced variation in the torque expression of preadjusted appliances.

The purpose of this article is to comprehensively investigate the sources of variation in the expression of torque in preadjusted appliances. Variables related to properties of materials were systematically analyzed, including (1) the inability to fill the slot because of the size difference of archwires and bracket slot, (2) irregularities from the manufacturing process of brackets precluding proper engagement, (3) differences in the stiffness of wire alloys engaged to the bracket slot, (4) variations between actual and reported bracket torque values, and (5) ligation modes, all of which might account for increased third-order clearance or bracket-archwire "play." The effect of these variations on the expression of torque is discussed, and the net buccolingual inclinations are provided as a function of wire size and composition for common bracket slot-archwire combinations. Most reports published on this issue indicate a loss of torque control as high as 100% of the prescribed value. Furthermore, the fallacy of transferring the ideal crown inclination to the torque prescribed in the bracket is illustrated, along with the underestimation of the prescribed torque relative to the proper tooth crown. The realistically required torque is analyzed to its constituent components, involving tooth inclination, compensation for the slot-wire play, and incomplete ligation with elastomeric ligatures. Based on the evidence available, it is proposed that a high-torque prescription should be selected to account for the lack of full expression of the prescribed torque that occurs clinically.

Dental Alloys↗
PubMed2004

Characterization and cytotoxicity of ions released from stainless steel and nickel-titanium orthodontic alloys.

The purpose of this study was to qualitatively and quantitatively characterize the substances released from orthodontic brackets and nickel-titanium wires and to comparatively assess the cytotoxicity of the ions released from these orthodontic alloys. Two full sets of stainless steel brackets of 20 brackets each (weight 2.1 g) and 2 groups of 0.018 x 0.025 Ni-Ti archwires of 10 wires each (weight 2.0 g) were immersed in 0.9% saline solution for a month. The immersion media were analyzed with inductively coupled plasma-atomic emission spectroscopy (ICP-AES), and the ionic content was statistically analyzed with 1-way analysis of variance (ANOVA). Human periodontal ligament fibroblasts and gingival fibroblasts were exposed to various concentrations of the 2 immersion media; nickel chloride was used as a positive control for comparison purposes. The cytotoxic or cytostatic activity of the media was investigated with the MTT and the DNA synthesis assays. The results of the cytotoxicity assay were analyzed with 2-way ANOVA and the Tukey test with solution and concentration variants as discriminating variables (alpha=0.05). The results indicated no ionic release for the nickel-titanium alloy aging solution, whereas measurable nickel and traces of chromium were found in the stainless steel bracket-aging medium. Concentrations of the nickel chloride solution greater then 2 mM were found to reduce by more than 50% the viability and DNA synthesis of fibroblasts; however, neither orthodontic materials-derived media had any effect on the survival and DNA synthesis of either cells.

Adult↗
PubMed2004

Structural conformation and leaching from in vitro aged and retrieved Invisalign appliances.

The objectives of this study were to investigate the structure of Invisalign appliances (Align Technology, Santa Clara, Calif) after intraoral exposure, and to qualitatively and quantitatively characterize the substances leached from the aligners after accelerated in vitro aging. Samples of Invisalign appliances were randomly selected from 10 patients before intraoral placement and after retrieval, and the prepared specimens were subjected to (1) bright-field optical reflection microscopy to study the surface morphology; (2) Fourier transform infrared microspectroscopy to characterize the in vivo changes in molecular composition induced on appliance surfaces, (3) scanning electron microscopy and energy dispersive X-ray microanalysis to identify the elemental composition of integuments formed on the surface, and (4) Vickers hardness (HV 200) testing. Another set of reference and retrieved appliances was subjected to artificial aging for 2 weeks, and the extracts were subjected to gas chromatography-mass spectroscopy. The retrieved appliances demonstrated substantial morphological variation relative to the as-received specimens involving abrasion at the cusp tips, adsorption of integuments, and localized calcification of the precipitated biofilm at stagnation sites. Buccal segments of retrieved appliances showed an increase in hardness, which might be attributed to mastication-induced cold work; however, the clinical implication of this effect on mechanotherapy is unknown. In vitro aged and retrieved appliances were found to leach no traceable amount of substances in an ethanol aging solution.

Adsorption↗
PubMed2004

Titanium orthodontic brackets: structure, composition, hardness and ionic release.

OBJECTIVES: The aim of the present study was to investigate the composition, morphology, bulk structure and ionic release of two brands of titanium orthodontic brackets: Orthos2 (Ormco, USA) and Rematitan (Dentaurum, Germany). METHODS: Five specimens of each group were examined with computerized X-ray microtomography, to reveal the morphology and structure of brackets, whilst resin-embedded and metallographically polished specimens were subjected to SEM/EDS analysis and Vickers microhardness measurements. Brackets were also maintained in 0.9% saline for 2 months and the ionic release in the immersion medium was determined with Inductively Coupled Plasma Atomic Emission Spectroscopy. The results of the hardness and ionic release measurements were statistically analyzed with two-way ANOVA and Tukey's test (alpha = 0.05). RESULTS: Orthos2 brackets consisted of two parts, the base (commercially pure Ti grade II) and the wing (Ti-6Al-4V alloy), joined together by laser welding, producing large gaps along the base-wing interface. The base was of lower hardness (Hv = 145), than the wing (Hv = 392) and incorporated a standard foil base-mesh pad. Rematitan brackets consisted of commercially pure Ti grade IV, with a single-piece manufacturing pattern of virtually identical hardness (p > 0.05) at the base and wings, featuring a laser-etched base-mesh pad. The hardness of the Rematitan brackets was significantly lower than the hardness of the Orthos2 wings, but double the hardness of the Orthos2 base. Released Ti levels were below the threshold level (1 ng/ml) of analysis for both materials, whilst traces of Al (3 ppm) and V (2 ppm) were found in the immersion media for Ti-6Al-4V alloy. SIGNIFICANCE: The structural and hardness differences found may influence the torque transfer characteristics from activated archwires to the brackets and the crevice corrosion potential at the base-wing interface (Orthos2). The detection of Al and V in the immersion medium (Orthos2) may imply a different biological response from the two types of Ti brackets.

Alloys↗
PubMed2004

Nickel content of as-received and retrieved NiTi and stainless steel archwires: assessing the nickel release hypothesis.

This study assesses the nickel content of as-received and retrieved stainless steel and NiTi archwires alloys. New and used brand-matched, composition-matched, and cross section-matched archwires were subjected to scanning electron microscopy and energy-dispersive electron probe microanalysis. Elemental analysis was performed on three randomly selected areas, and the nickel content, expressed as ratios of Ni/Ti (in NiTi wires) or Ni/Fe (in stainless steel), was statistically analyzed with a t-test (alpha = .05). No changes were detected with respect to Ni content ratios between as-received and retrieved NiTi or stainless steel wires, suggesting an absence of nickel release. Wear and delamination phenomena on the wire surface and the formation of galvanic couple between the stainless steel wires and bracket brazing materials intraorally may modify the corrosion susceptibility of the wire alloys in clinical conditions.

Corrosion↗
PubMed2004

Color stability of orthodontic adhesive resins.

Color alteration of adhesive during treatment and after debonding may be implicated in long-term enamel discoloration. The aim of this study was to assess the color stability of light-cured and chemically cured adhesives subjected to artificial photoaging. Disk-shaped specimens of adhesives were colorimetrically evaluated before and after artificial photoaging using an ISO-recommended protocol. The measurement variable was the color change (deltaE) of adhesives induced by artificial, accelerated photoaging. The deltaE values derived from the two color recordings for the materials at pre- and postaging intervals were statistically analyzed with a one-way analysis of variance (ANOVA), with the adhesive brand serving as a discriminating variable. Differences among groups were further investigated using the Tukey multiple comparisons test (alpha = .05). To establish the statistical significance of the difference of the deltaE values of each adhesive and the deltaE threshold for clinical detection, a paired t-test was used (P = .05). All adhesives exhibited color change, which in some cases exceeded the clinically detectable color change limit. The extent of the color alterations of aged bonding systems may contribute to enamel discoloration after treatment.

Analysis of Variance↗
PubMed2004

Elemental composition of brazing alloys in metallic orthodontic brackets.

The aim of this study was to assess the elemental composition of the brazing alloy of representative orthodontic brackets. The brackets examined were Gemini (3M, Unitec, Monrovia, Calif), MicroLoc (GAC, Bohemia, NY), OptiMESHxrt (Ormco, Glendora, Calif), and Ultratrim (Dentarum, Ispringen, Germany). Four metallic brackets for each brand were embedded in epoxy resin and after metallographic grinding and polishing were cleaned in a water ultrasonic bath. Scanning electron microscopy and energy-dispersive x-ray microanalysis (EDS) were used to assess the quantitative composition of the brazing alloy. Four EDS spectra were collected for each brazing alloy, and the mean value and standard deviation for the concentration of each element were calculated. The elemental composition of the brazing alloys was determined as follows (percent weight): Gemini: Ni = 83.98 +/- 1.02, Si = 6.46 +/- 0.37, Fe = 5.90 +/- 0.93, Cr = 3.52 +/- 0.34; MicroLoc: Ag = 42.82 +/- 0.18, Au = 32.14 +/- 0.65, Cu = 24.53 +/- 0.26, Mg = 1.12 +/- 0.33; OptiMESHxrt: Au = 67.79 +/- 0.97, Fe = 15.69 +/- 0.29, Ni = 13.01 +/- 0.93, Cr = 4.01 +/- 0.35; Ultratrim: Ag = 87.97 +/- 0.33, Cu = 10.51 +/- 0.45, Mg = 1.29 +/- 0.63, Zn = 1.13 +/- 0.24. The findings of this study showed that different brazing materials were used for the different brands, and thus different performances are expected during intraoral exposure; potential effects on the biological properties also are discussed.

Dental Alloys↗
PubMed2004

Enamel surface roughness following debonding using two resin grinding methods.

The purpose of this study was to assess quantitatively the roughness of the enamel surface following debonding using two resin removal methods. The enamel surface of 30 premolar crowns was covered with black tape with a 3 mm window on the middle buccal third to standardize the area of analysis. The initial enamel surfaces were subjected to profilometry, registering four roughness parameters (Ra, Rq, Rt and Rz). The brackets were bonded to the plaster-embedded enamel surfaces with a chemically cured, no-mix adhesive, and debonded after 1 week. Resin removal in half of the specimens was performed with an eight-bladed carbide bur, and in the other half with an ultra-fine diamond bur, both attached to a high speed hand piece; a second profilometric measurement was made after resin removal. Finishing of all surfaces was achieved with Soflex discs and a third registration of roughness followed. The duration of each resin removal protocol was also recorded. The results were analysed with two-way ANOVA and the Newman-Keuls test with the two resin grinding modes and the three intervals serving as discriminating variables (n = 15). For the duration results, a one-way ANOVA was used. Significant differences (P < 0.05) were observed with respect to enamel roughness parameters between the two resin grinding methods used, while there was no consistent roughness-reducing effect of finishing with Soflex discs. Resin removal with a diamond bur was achieved in approximately half the time compared with the eight-bladed bur. The increase in most roughness variables induced by the debonding procedures was not reversed at the end of the finishing stage, regardless of the resin removal protocol used, suggesting an irreversible effect on enamel texture.

Analysis of Variance↗
PubMed2004

Plastic brackets: hardness and associated clinical implications.

AIM: To assess the Vickers hardness of plastic brackets, after in vitro aging. The morphology and structure of corresponding retrieved brackets were also studied to assess the reliability of in vitro set-up in imposing effects comparable to intraoral aging. MATERIALS AND METHODS: Four types of plastic brackets were selected. Specimens were immersed in a buffer solution to induce artificial aging; brackets of two groups were retrieved after orthodontic treatment. The wings of brackets were subjected to Knoop hardness testing, and scanning electron microscopy was employed to study the morphology and microstructure of retrieved brackets. The results were statistically analyzed by two-way analysis of variance and Tukey test (alpha = 0.05). RESULTS: Differences were identified between the brands of brackets, but not between the new and in vitro-aged appliances. The retrieved appliances showed significant reduction in hardness when compared with their as-received counterparts. Evidence of degradation was seen in the retrieved appliances. CONCLUSIONS: The inability of ex vivo experimental configuration to simulate clinical conditions is stressed; several clinical implications related to torque control, friction, and tie-wing strength of brackets are discussed.

Buffers↗
PubMed2003

Characterization of as-received, retrieved, and recycled stainless steel brackets.

AIM: The purpose of the present study was to investigate the composition and to assess the microhardness and structure of as received, retrieved, and recycled stainless steel brackets. MATERIALS AND METHODS: New, used, and recycled brand-, slot size-, and prescription-matched appliances were subjected to scanning electron microscopy (SEM), energy dispersive (EDS) electron probe microanalysis, metallographic analysis, and Vickers microhardness testing. Elemental analysis was performed on randomly selected bulk material base and wing areas. Basic metal content and microhardness results were statistically analyzed using a two-way ANOVA and the Tukey test, with treatment (as received, retrieved, and recycled) and bracket region (base, wing) serving as discriminating variables (alpha = 0.05). RESULTS: The results showed that there was no alteration in the bulk composition of the brackets among the three conditions. In contrast, differences were noted between bracket base and wing with respect to elemental composition among all groups, implying that the base and wings were manufactured from different alloys. The metallographic etching identified no difference in grain structure between the bracket base and wing components for all groups, regardless of treatment. Vickers microhardness demonstrated significant differences in hardness between base and wing for all groups and between recycled and retrieved states for the wing component.

Electron Probe Microanalysis↗
PubMed2003

Metallographic structure and hardness of titanium orthodontic brackets.

AIM: To determine the elemental composition, microstructure, and hardness of two different brands of titanium (Ti) orthodontic brackets. MATERIALS AND METHODS: Four specimens of each brand were embedded in epoxy resin and, after metallographic grinding and polishing, were studied under a metallographic microscope. The bonding base morphology of each bracket was studied in as-received brackets by scanning electron microscopy. Energy dispersive x-ray microanalysis (EDS) was used on polished specimens to assess the elemental composition of base and wing bracket components, and the brackets were subjected to metallographic etching to reveal the metallurgical structure. The same specimen surfaces were used for assessment of the Vickers hardness. The results were statistically analyzed by two-way analysis of variance (ANOVA) with the bracket brand and bracket region (base, wing) serving as discriminating variables, whilst further group differences were investigated with Tukey's multiple comparison test at the alpha = 0.05 level of significance. RESULTS: Metallographic imaging revealed that the Orthos2 brackets (Ormco, Glendora, CA, USA) consist of two parts joined together by laser welding, with large gaps along the base wing interface, whereas Rematitan brackets (Dentaurum, Ispringen, Germany) are single-piece appliances. Ti was the only element identified in Rematitan and Orthos2 base materials, while aluminium (Al) and vanadium (V) were also found in the Orthos2 wing component. Metallographic analysis showed the presence of a + b phase for Orthos2 and plate-like grains for Rematitan. The results of the Vickers hardness testing were: Orthos2 (wing): 371 +/- 22, Rematitan (wing): 272 +/- 4, Rematitan (base): 271 +/- 16, Orthos2 (base): 165 +/- 2. CONCLUSION: The findings of the present study suggest that there are significant differences in composition, microstructure and hardness between the two commercial types of Ti brackets tested; the clinical implications of the findings are discussed.

Alloys↗
PubMed2003

Salivary metal levels of orthodontic patients: a novel methodological and analytical approach.

The purpose of this study was to qualitatively and quantitatively assess the nickel, chromium, and ferrous levels in a population of 17 orthodontic patients undergoing treatment, compared with seven untreated individuals, employing a novel methodological approach and a new analytical technique. Salivary samples obtained from patients before and after rinsing with double distilled water were processed for Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES) for simultaneous estimation of the concentration of the metallic elements. No statistically significant difference was detected between control and patient groups with respect to salivary metal content, regardless of element. The range of salivary metal levels found did not exceed those of daily intake through food and air. The lack of a continuous monitoring scheme for salivary metal concentrations in real time may impose substantial obstacles to defining the release rate of metals in vivo. The results of this study emphasize the necessity of incorporating the dimension of time in assessing the release potential of orthodontic alloys.

Adolescent↗
PubMed2002

In vivo aging of orthodontic alloys: implications for corrosion potential, nickel release, and biocompatibility.

Despite the large number of studies investigating nickel release from orthodontic stainless steel and nickel-titanium alloys, there is a lack of conclusive evidence with respect to the composition and kinetics of the corrosive products released. The objective of this review is to address the critical issues of corrosion potential and nickel leaching from alloys by investigating the effect of intraoral conditions on the surface reactivity of the materials. After an overview of fundamentals of metallurgical structure of orthodontic alloys, we provide an analysis of corrosion processes occurring in vivo. We present recent evidence suggesting the formation of a proteinaceous biofilm on retrieved orthodontic materials that later undergoes calcification. We illustrate the vastly irrelevant surface structure of in vivo- vs in vitro-aged alloys and discuss the potential implications of this pattern in the reactivity of the materials. Finally, we present a comprehensive review of the issue of nickel release, based on three perspectives: its biologic effects, the methods used for studying its release, and nickel-induced hypersensitivity in orthodontic patients.

Corrosion↗
PubMed2002

Nickel content of as-received, retrieved, and recycled stainless steel brackets.

The purpose of this study was to investigate the composition of as-received, retrieved, and recycled stainless steel brackets. New, used, and recycled brand-matched, slot size-matched, and prescription-matched appliances were subjected to scanning electron microscopy and energy dispersive electron probe microanalysis. Elemental analysis was performed on randomly selected surface bracket base and wing areas, and metal content was statistically analyzed with the 2-way ANOVA and the Tukey test, with treatment (as-received, retrieved, and recycled) and bracket regions (base and wing) serving as discriminating variables (alpha = 0.05). The results showed that there was no difference in the surface composition of the base; however, surface area-wing analysis indicated that nickel content was decreased in retrieved and recycled specimens, implying that an ionic release effect occurred in vivo. Differences were noted between bracket base and wing with respect to elemental composition for the same brackets, implying that the base and wings are manufactured from different alloys.

Analysis of Variance↗